Layer 1

How the storage target is calculated

The tool produces a planning target in terabytes. That is the amount of capacity to plan for after growth and headroom — not a promise of post-RAID usable space.

The formula

current + (photos/year + videos/year) × horizon → × headroom → TB

Gigabytes in, terabytes out. Division is by 1,000. Matching uses the raw figure; one-decimal rounding is display only, so 7.96 TB does not jump a bay rule because it looked like 8.0 on screen.

Headroom

• Normal — multiplies by 1.2 (20% extra)
• High — multiplies by 1.5 (50% extra)

Editorial rules (provenance R). Not taken from a manufacturer document.

What we omit

We do not apply a filesystem or system-reserve overhead multiplier. Exact usable capacity after RAID/SHR depends on drive count and size, which are not known yet. Inventing a fixed percentage would overstate the evidence. When you later pick disks, the vendor’s own usable calculator can refine the number.

What we will not invent

• No GB-per-person defaults
• No assumed photo or video sizes — you supply annual growth
• No invented overhead dressed as verified manufacturer data
• Missing or invalid inputs return UNKNOWN

Why start here

Most people guess a terabyte number, then discover usable capacity after redundancy is lower than expected. Starting from household facts reduces that surprise without pretending we already know the drive configuration.